Piezoelectric devices have a wide range of uses in science and industry. One exemplary application of a piezoelectric device is a surface acoustic wave (SAW) device. Such SAW devices may be used, for example, as filters, oscillators and transformers, all of which are devices that are based on the transduction of acoustic waves. SAW devices are generally constructed using a crystalline piezoelectric material which has necessary properties to produce a surface acoustic wave when the device input is stimulated using an electronic signal. Electronic devices including SAW devices therein, will include one or more interdigital transducers (IDTs) to convert the surface acoustic waves to electrical signals (and vice versa), relying on the piezoelectric effect of the crystalline piezoelectric material. One common application of SAW devices is in mobile phones.
SAW devices may also be used as sensors in many areas, including, for example, chemical, optical, thermal, pressure, acceleration, torque and biological. One particular use of SAW devices as a sensor involves the application of a bio-coating to the SAW device to enable the device to detect the presence of biological agents, such as particular viruses and bacteria. SAW technology could be used, for example, to produce an infectious disease detection cartridge, and in one instance this detection cartridge may be low-cost enough to be disposable. A particular challenge in this regard, however, is how to interface, mechanically and electrically, to the sensor itself.
One method of making an electrical connection to a piezoelectric device is wire bonding, e.g., welding. However, when mounting piezoelectric devices, and in particular a bio coated SAW device, to a circuit board, there are several considerations which must be addressed. For example, a bio-coated SAW device is sensitive to heat. While a SAW device, generally, is not heat sensitive, coatings incorporating such biological materials may be damaged by exposure to high temperatures. Wire bonding, which as mentioned is conventionally used for other SAW devices, involves steps that would heat the device to an unacceptable degree in the context of a biosensor. Thus, wire bonding cannot be used for mounting a bio-coated SAW device to the circuit board. Further, piezoelectric devices in general are, by their nature, sensitive to mechanical stress. Stress induced by mechanical contact during mounting must be minimized. Also, a reliable, low-loss connection is needed for the radio frequency (RF) signal input and output from the device. Of course, any successful commercialization requires the mounting method to be low cost as well.
Accordingly, there is a need and desire for a low-cost, reliable method of mounting piezoelectric devices, and in particular a bio-coated SAW device, e.g., a biosensor, on a PC board.